Who Stole Kathy Young? by Margaret Goff Clark, 1980.

Kathy Young has had her share of problems.  Her mother died a year and a half ago, and now, her father has a housekeeper with a sour personality.  A couple of months after her mother’s death, Kathy was seriously ill, and her illness caused her to lose most of her hearing.  She now depends on a hearing aid and her improving lip-reading and sign language abilities.

This summer, Kathy’s best friend, Meg, is staying with her while her parents are on a trip to Switzerland.  Meg was of great help to Kathy when she was trying to adjust to her hearing loss, practicing sign language with her during her special lessons.  Kathy’s dream is to become an artist, but Meg now wants to be a teacher for the deaf, like the teacher who taught Kathy.  Kathy is still very unsure of her abilities to cope with her deafness.  She had the opportunity to attend a special art workshop over the summer but passed it up because she was worried about whether she would be able to communicate with and understand her teacher and the other students, and she knew Meg couldn’t attend to help her.

Kathy has been enjoying Meg’s summer visit, but the girls have noticed something odd.  It seems like a couple of strangers, a man and a woman, have been hanging around everywhere they go.  Meg is worried about it, but Kathy doesn’t want to worry her father.  She thinks that they’re probably tourists, like the housekeeper said.  They nickname the strangers Heron and Toad because of their appearances.

One day, Kathy is kidnapped!  Some men in a van stop to ask her directions and when she tries to explain where they have to go, they pull her inside and drug her!  Meg witnesses the kidnapping, but is standing too far away to help Kathy.

When Kathy wakes up from being drugged, she finds herself on a boat.  Her abductors have cut her hair and changed her shirt to disguise her from anyone who might spot her.  They’ve also taken her hearing aid, hoping to render her helpless and keep her from finding out their plans because she can’t hear them.  However, Kathy isn’t as helpless as they think.  She can still read lips, and she can still think.

Kathy learns to rely on herself and her own wits as she tries to gather as much information as she can about her kidnappers and to figure out how she can save herself.  Through this experience, she develops more self-confidence, realizing that she can do more and handle more than she had thought was possible.

While Kathy is struggling in captivity and her father is dealing with the police and the ransom demand, her friend Meg is trying desperately to find her.  The story alternates viewpoints between the two girls as Meg aids the investigation into Kathy’s disappearance and puts together clues that Kathy leaves for her as her abductors move her from place to place.  The mastermind behind the kidnapping plot is closer to home than they think.

The book is available to borrow and read for free online through Internet Archive.